This invention relates to light guides, in particular but not exclusively to light guide illumination sources for illuminated vehicle instrument displays.
Instrument panel displays are known in which a light source or sources illuminate one side of a generally opaque panel marked with translucent characters or apertures through which light passes to reveal bright characters against the opaque background. Such a system makes inefficient use of the light since the entire reverse of the panel is illuminated and only a relatively small percentage of the light passes through the panel.
Alternative systems have been proposed in which a light guide conducts light from a source and directs it onto the front of a panel to reflectively illuminate fluorescent characters. Another light guide system has been devised in which the light guide passes behind a panel and the light is selectively directed by prismatic projections onto a convex reflector aligned with translucent characters in the panel which dispenses the light through the character. These light guide systems are inefficient at the light input stage which essentially consists of a plane surface abutting a lamp, and furthermore the co-operative parts, i.e. the lamp, reflectors and prismatic extensions require alignment.